igneous
Riverstone (likely Basalt or Greywacke)
Extrusive Magmatic Basalt
Hardness: 6-7 (Mohs); Color: Dark grey to charcoal when dry, black when wet; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9-3.1
- Hardness
- 6-7 (Mohs)
- Color
- Dark grey to charcoal when dry, black when wet
- Luster
- Dull/Matte
Identified More igneous →
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark grey to charcoal when dry, black when wet; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9-3.1
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. This specific specimen has been smoothed by fluvial (river) or coastal erosion over centuries.
Uses & applications
Used in landscaping, construction aggregate, hot stone therapy, and as aquarium decor.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Smoothed river stones like this are often millions of years old.
Field identification & locations
Identify by its heavy weight (high density), fine-grained texture, and lack of visible crystals. Commonly found in riverbeds, glacial tills, and along volcanic coastlines.
